Method and arrangement for avoiding loss of error-critical non real time data during certain handovers

ABSTRACT

A method is disclosed for a mobile station for performing a handover from a first network connection to a second network connection. A mobile telecommunication system provides for non-real time telecommunication connections over a radio interface between mobile stations and the fixed parts of the mobile telecommunication system. At least one active non-real time telecommunication connection is between a mobile station and the fixed parts of the mobile telecommunication system is suspended ( 704 ) before performing a handover ( 702 ′) from the first network connection to the second network connection. After the new connection has been established the suspended non-real time telecommunication connection are resumed ( 705 ).

TECHNOLOGICAL FIELD

The invention concerns generally the protocol structures that are usedto arrange the communication between a mobile terminal and apacket-switched network. Especially the invention concerns the optimalcomposition of such structures from the point of view of minimized riskof losing certain types of data in certain handover situations on onehand and reduced complexity on the other.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates the known data protocol stacks that are applied in apacket-switched communication connection where one end is a MobileStation (MS) and the communication takes place over a GPRS network(General Packet Radio Service) through a Base Station Subsystem (BSS), aServing GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN).The protocol layers where the peer entities are in the MS and the BSSare the physical layer 101 that employs the GSM cellular radio system(Global System for Mobile telecommunications), the Media Access Control(MAC) layer 102 and the Radio Link Control layer 103 which sometimes isregarded as only a part of the MAC layer 102—hence the dashed linebetween them. The protocol layers where the peer entities are in the BSSand the SGSN are the L1bis layer 104, the Network Service layer 105 andthe BSS GPRS Protocol (BSSGP) layer 106.

The layers for which the peer entities are in the MS and the SGSN arethe Logical Link Control (LLC) layer 107 and the SubNetwork DependentConvergence Protocol (SNDCP) layer 108. It should be noted that onlydata or user plane protocols are shown in FIG. 1; a completeillustration of protocols would include the Layer 3 Mobility Management(L3MM) and Short Message Services (SMS) blocks on top of the LLC layer107 in parallel with the SNDCP layer 108. Additionally there are theknown Session Management (SM) and Radio Resource management (RR)entities that are not located on top of the LLC layer. At the interfacebetween the SGSN and the GGSN there are the Layer 1 (L1) layer 109, theLayer 2 (L2) layer 110, a first Internet Protocol (IP) layer 111, theUser Datagram Protocol/Transport Control Protocol (UDP/TCP) layer 112and the GPRS Tunneling Protocol (GTP) layer 113. Between the MS and theGGSN there are the X.25 layer 114 and a second Internet Protocol layer115. An application layer 116 in the MS will communicate with a peerentity that is located for example in another MS or some other terminal.

Proposals for the future UMTS (Universal Mobile TelecommunicationSystem) have suggested similar protocol structures for the communicationbetween mobile stations, Radio Network Controllers (RNCs) and servicenodes of packet-switched networks, with small changes or modificationsin the designations of the devices, layers and protocols. It is typicalto protocol structures like that in FIG. 1 that each layer has anexactly determined set of tasks to perform and an exactly determinedinterface with the next upper layer and the next lower layer. A certainamount of memory and processing power must be allocated in the devicestaking part in the communication to maintain the layered structure andaccomplish the tasks of each layer. It is therefore easily understoodthat the more complicated the structure of layered protocols, the morecomplicated the required software and hardware implementation.Complexity is disadvantageous in terms of costs incurred in design andmanufacture and it increases the possibility of design errors.Additionally, in battery-driven mobile terminals it is a continual aimto reduce power consumption and diminish physical size, whereby a moresimplified structure of protocol layers would create advantage.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand arrangement that would accomplish the tasks of known communicationprotocol arrangements but with a simpler protocol structure.

The objects of the invention are accomplished by replacing certain partsof the protocol structure by a temporary suspension of certaincommunications for the duration of a handover.

The method according to the invention is characterised by that itcomprises the steps of

-   -   suspending at least one active non-real time telecommunication        connection between a mobile station and the fixed parts of a        mobile telecommunication system,    -   performing a handover from a first network connection to a        second network connection and    -   resuming the suspended non-real time telecommunication        connection.

The invention also concerns a mobile station arranged to perform ahandover according to the above-described method.

The invention relates closely to the observation that the role ofcertain layers in many protocol structures is of minor practical valueand is limited to certain measures for avoiding loss of data during ahandover. If the data concerned allows for some additional delays to becaused on its path from the transmitting device to the receiving device,such protocol layers may be omitted altogether by simply suspending thetransmission of data when a handover is about to take place and resumingnormal operation after the handover has been successfully completed.

In the GPRS example presented in the description of prior art theprotocol layer that can be omitted by employing thesuspension-resumption mechanism is the LLC layer. We may note that theRLC layer is capable of performing all required error correction tasksover the radio interface in normal operation and the role of LLC hasmainly been related to handovers between different BSCs (Base StationControllers), where error-critical (but not delay-critical) data hasneeded a mechanism for avoiding loss of data. In the proposed UMTS asimilar need has existed in handovers between different RNCs or SGSNs(often designated as 3GSGSNs or 3rd Generation SGSNs). If we remove thisneed by temporarily suspending the transmission of such error-criticaldata altogether for the duration of that time interval where loss ofdata could otherwise occur, the error-correcting functions of the LLClayer become superfluous.

The LLC layer has also had certain responsibilities for flow control.According to the invention the RLC layer may take care of all flowcontrol between the mobile station and a base station controller or aradio network controller (or generally the radio access network), andlocal flow control mechanisms may be employed for controlling the flowover the interface between the radio access network and a core network.In UMTS the latter is known as the Iu interface.

BRIEF DESCRIPTION OF DRAWINGS

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

FIG. 1 illustrates the known protocol stacks in a GPRS implementation,

FIG. 2 illustrates the known functional model of an LLC layer,

FIG. 3 illustrates a functional model that would replace the LLC layeraccording to the invention,

FIG. 4 illustrates an arrangement of protocol stacks according to theinvention,

FIGS. 5 a to 5 c illustrate an inter-RNC, intra-SGSN handover accordingto the invention,

FIGS. 6 a to 6 c illustrate an inter-RNC, inter-SGSN handover accordingto the invention and

FIGS. 7 a and 7 b show a comparison between a prior art method and amethod according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

We will illustrate the applicability of the invention in connection withthe known GPRS system. However, the presented examplary embodiments donot limit the applicability of the invention to any specific system. Asa background to the invention we will first consider some knowncharacteristics of the GPRS system.

The general packet radio service (GPRS) is a new service to the GSMsystem, and is one of the objects of the standardization work of the GSMphase 2+ at the ETSI (European Telecommunications Standards Institute).The GPRS operational environment comprises one or more subnetworkservice areas, which are inter-connected by a GPRS backbone network. Asubnetwork comprises a number of packet data service nodes (SN), whichin this application will be referred to as serving GPRS support nodes(SGSN), each of which is connected to the mobile telecommunicationssystem in such a way that it can provide a packet service for mobiledata terminals via several base stations, i.e. cells. The intermediatemobile communication network provides packet-switched data transmissionbetween a support node and mobile data terminals. Different subnetworksare in turn connected to an external data network, e.g. to a publicswitched data network (PSDN), via GPRS gateway support nodes (GGSN). TheGPRS service thus allows to provide packet data transmission betweenmobile data terminals and external data networks when the appropriateparts of a mobile telecommunications system function as an accessnetwork.

In order to access the GPRS services, a MS shall first make its presenceknown to the network by performing a GPRS attach. This operation makesthe MS available for SMS (Short Message Services) over GPRS, paging viaSGSN, and notification of incoming GPRS data. More particularly, whenthe MS attaches to the GPRS network, i.e. in a GPRS attach procedure,the SGSN creates a mobility management context (MM context). Also theauthentication of the user is carried out by the SGSN in the GPRS attachprocedure. In order to send and receive GPRS data, the MS shall activatethe packet data address that it wants to use, by requesting a PDPcontext activation procedure, where PDP comes from Packet Data Protocol.This operation makes the MS known in the corresponding GGSN, andinterworking with external data networks can commence. More particularlya PDP context is created in the MS and the GGSN and the SGSN. The PDPcontext defines different data transmission parameters, such as the PDPtype (e.g. X.25 or IP), PDP address (e.g. X.121 address), quality ofservice (QoS) and NSAPI (Network Service Access Point Identifier). TheMS activates the PDP context with a specific message, Activate PDPContext Request, in which it gives information on the TLLI, PDP type,PDP address, required QoS and NSAPI, and optionally the access pointname (APN).

The quality of service defines how the packet data units (PDUs) arehandled during the transmission through the GPRS network. For example,the quality of service levels defined for the PDP addresses control theorder of transmission, buffering (the PDU queues) and discarding of thePDUs in the SGSN and the GGSN, especially in a congestion situation.Therefore, different quality of service levels will present differentend-to-end delays, bit rates and numbers of lost PDUs, for example, forthe end users.

Currently the GPRS allows for only one QoS for each PDP context.Typically a terminal has only one IP address, so conventionally it mayrequest for only one PDP context. There is recognised the need formodifying the existing systems so that a PDP context could accommodateseveral different QoS flows. For example, some flows may be associatedwith E-mail that can tolerate lengthy response times. Other applicationscannot tolerate delay and demand a very high level of throughput,interactive applications being one example. These different requirementsare reflected in the QoS. Intolerance to delay must usually beassociated with a relatively good tolerance for errors; correspondinglya very error-critical application must allow for long delays, because itis impossible to predict how many retransmission attempts it will taketo achieve the required high level of correctness. If a QoS requirementis beyond the capabilities of a PLMN, the PLMN negotiates the QoS asclose as possible to the requested QoS. The MS either accepts thenegotiated QoS, or deactivates the PDP context.

Current GPRS QoS profile contains five parameters: service precedence,delay class, reliability, and mean and peak bit rates. Serviceprecedence defines some kind of priority for the packets belonging to acertain PDP context. Delay class defines mean and maximum delays for thetransfer of each data packet belonging to that context. Reliability inturn specifies whether acknowledged or unacknowledged services will beused at LLC (Logical Link Control) and RLC (Radio Link Control) layers.In addition, it specifies whether protected mode should be used in caseof unacknowledged service, and whether the GPRS backbone should use TCPor UDP to transfer data packets belonging to the PDP context.Furthermore, these varying QoS parameters are mapped to four QoS levelsavailable at the LLC layer.

FIG. 2 is a functional model of a known LLC protocol layer 201,corresponding to the blocks 107 in FIG. 1. Block 202 represents theknown lower layer (RLC/MAC; Radio Link Control/Media Access Control)functions that are located below the LLC layer 201 in the protocol stackof a mobile station MS. Correspondingly block 203 represents the knownlower layer (BSSGP) functions that are located below the LLC layer 201in a serving GPRS support node SGSN. The interface between the LLC layer201 and the RLC/MAC layers 202 is called the RR interface and theinterface between the LLC layer 201 and the BSSGP layers 203 is calledthe BSSGP interface.

Above the LLC layer there are the known GPRS Mobility Managementfunctions 204 (also known as the Layer 3 Mobility Management functionsor L3MM), SNDCP functions 205 and Short Messages Services functions 206.Each one of these blocks has one or more interfaces with the LLC layer201, connecting to its different parts. The Logical Link ManagementEntity 207 has an LLGMM control interface (Logical Link—GPRS MobilityManagement) with block 204. Mobility management data is routed through aLLGMM data interface between block 204 and the first Logical Link Entity208 of the LLC layer. The second 209, third 210, fourth 211 and fifth212 Logical Link Entities connect to block 205 through the correspondinginterfaces; according to the QoS levels handled by each of the LogicalLink Entities the interfaces are known as QoS 1, QoS 2, QoS 3 and QoS 4.The sixth Logical Link Entity 213 of the LLC layer connects to block 206via an LLSMS interface (Logical Link—Short Messages Services). TheService Access Point Identifiers or SAPIs of the first 208, second 209,third 210, fourth 211, fifth 212 and sixth 213 Logical Link Entities arerespectively 1, 3, 5, 9, 11 and 7. Each one of them is connected insidethe LLC layer to a multiplexing block 214, which handles the connectionsthrough the RR interface to block 202 and further towards the mobilestation as well as the connections through the BSSGP interface to block203 and further towards the SGSN. The connection between themultiplexing block 214 and the lower layer block 202 in the direction ofthe MS may be described as a “transmission pipe”.

FIG. 3 illustrates an arrangement according to the invention where theLLC layer has been completely omitted. The upper layers comprise a MM/RRpart 301 for known mobility and radio resource management, an SMS part303 for processing data related to short messages, as well as a part302′ for processing the received data and data to be transmittedaccording to other functionalities. “Local” multiplexing/-demultiplexingis performed at the upper layers in blocks 304 to 308 so that there isonly one transmission pipe for control information between the MM/R part301 and the lower layers, one transmission pipe for SMS-relatedinformation between the SMS part 303 and the lower layers, and onetransmission pipe for each quality of service class between the otherfunctionalities part 302 and the lower layers. Multiplexing is shown inFIG. 3 as taking place in separate functional blocks; however, it may bean inherent part of for example one or several functionalities in theother functionalities part 302.

The RLC/MAC layer is located directly under the upper layers in FIG. 3.It performs the known RLC/MAC functions for each flow of information forwhich there is a connection between it and the upper layers. The MACfunctions consist of procedures for sharing the common radio channelsbetween mobile stations as well as allocations and disallocations ofdedicated radio channels. The RLC functions comprise the composing anddecomposing of RLC blocks, detecting corrupted RLC blocks and arrangingfor the retransmission of corrupted blocks when appropriate. In UMTS thethe concept of an RLC unit is unidirectional and reserved for oneinformation flow only, so the widely interpreted RLC layer in theprotocol structure will accommodate a pair of RLC units for each activeflow of information. The multiplexing and demultplexing of the RLCblocks belonging to different flows of information takes place on thephysical layer, which is represented by block 315 in FIG. 3. In a spreadspectrum system it is advantageous to multiplex all flows of informationrelated to a certain mobile terminal onto a single code channel. Fromthe published standardisation work of the UMTS there is known a physicallayer that is applicable to perform the operations represented by block315.

FIG. 3 as such is only applicable to the mobile station, because thereis an RLC/MAC layer under the higher-order layers. However, it is easyto generalise the arrangement of FIG. 3 so that there may be a BSSGPlayer under the higher-order layers, resulting in an arrangementapplicable to a SGSN. Also in that case there must be an additionalstage of multiplexing/demultiplexing at the physical level, like block315 in FIG. 3.

FIG. 4 illustrates the inventive structure of protocol stacks which iscomparable to the known arrangement of FIG. 1. It is noted that there isno LLC layers in the mobile station or the SGSN, the physical layerbetween the mobile station and the RAN has been replaced by a UMTSphysical layer 401, the BSSGP layer between the RAN and the SGSN hasbeen replaced by a corresponding UMTS layer preliminarily known as theRANGP (RAN GPRS Protocol) layer 402, and the MAC, RLC, SNDCP, NetworkService and L1bis layers have been adapted according to the guidelinesgiven above in association with FIG. 3.

Next we will describe some handover situations where a mobile stationand the network will apply the principle of temporarily suspendingerror-critical communications according to the invention. FIG. 5 aillustrates a situation where the mobile station 501 has amacrodiversity connection with two RNCs (Radio Network Controllers)network so that the first RNC 502 is the so-called serving RNC and thesecond RNC 503 is the so-called drifting RNC. The interface between thetwo RNCs is called the Iur interface. From the serving RNC 502 there isa connection to a SGSN 504 over a so-called Iu interface, and from theSGSN there is a connection to a GGSN 505. A generalisation of thearrangement of FIG. 5 a is the case where the second RNC is just a “new”serving RNC regardless of whether it was firstly a drifting RNC or not.Drifting RNCs relate only to macrodiversity; if no macro-diversity isapplied there will be an “old” serving RNC and a “new” serving RNC (or,in second generation systems, an “old” BSS and a “new” BSS) with littlesimultaneous service from both of them to the mobile station.

In FIG. 5 b either the mobile station 501 or some network device in theradio access network (not shown) where the serving RNC 502 is locatednotices that the direct connection between the mobile station and theserving RNC is critically weakening or has been severed, so a handoverto the second RNC 503 is inevitable. According to the invention, thehandover is started by requesting all such active services to besuspended which require a high level of correctness and tolerate longdelays. In a GPRS type arrangement the suspension of services wouldrequire suspending whole PDP contexts, because the PDP context can onlyhave one QoS. In a UMTS type arrangement it suffices to suspends thoseQoS flows for which the QoS allows for (delay tolerance) and evenrequires (correctness) the suspension. To retain generality we will usethe word “service” for the entities that will be suspended. It will bemost advantageous to define beforehand, in a standardised specification,a threshold value either for required correctness or for allowed delaysor for both so that only those active services will be suspended forwhich the required correctness or allowed delay or both exceed thethreshold value(s).

After the suspension of the selected active services the network willestablish a new connection over the Iu interface between the second RNC503 and the SGSN 504. Simultaneously communication on the non-suspendedservices may continue. Typically there will be some RLC level buffers inat least one of the devices taking part in the communication that needto be emptied before the second RNC may be designated as the servingRNC. The situation illustrated in FIG. 5 c may only become relevantafter all such RLC buffers have been emptied and the new connection overthe Iu interface between the second RNC and the SGSN has beenestablished. At that moment the suspended services may be released sothat communication over them will continue normally. In FIG. 5 c thesecond RNC 503 is the serving RNC and the old connection over the Iuinterface between the first RNC 502 and the SGSN 504 has beenterminated.

In FIG. 5 c it has been assumed that the handover was not associatedwith a complete severance of the direct connections between the mobilestation 501 and the first RNC 502. Consequently the connection over theIur interface between the RNCs is not terminated and the first RNCcontinues to operate as a drifting RNC. Sooner or later, especially ifthe mobile station continues the movement that caused the directconnections to the first RNC to weaken, these direct connections willfall under the level of acceptable quality so that they are completelyreleased and the connection over the Iur interface between the RNCs isterminated.

FIGS. 6 a to 6 c describe a handover situation where the new RNCoperates under a new SGSN. Such a handover is called an inter-RNC,inter-SGSN handover. Here we have expected that an Iur interface existseven between RNCs that operate under different SGSNs; this is not arequirement associated with the invention, because the invention worksequally well without any connections between the RNCs. FIG. 6 acorresponds to FIG. 5 a with the sole exception that the second RNC 601belongs to the domain of a second SGSN 602. At some stage it is againnoticed that a handover from the first RNC to the second RNC will berequired. The operation starts with the suspension of error-critical,delay-tolerant PDP contexts as described above. According to FIG. 6 b,the controlling responsibility remains in the first RNC 502 and thefirst SGSN 504 during the time it takes the mobile station to registrateunder the second SGSN 602 and the latter to set up a new GTP bearer withthe GGSN 505. The first SGSN 504 will also transmit all informationrelated to the connections to be transferred to the second SGSN 602, asillustrated by an arrow in FIG. 6 b. Thereafter the controllingresponsibilities may be moved to the second RNC 601 and the second SGSN602 as illustrated in FIG. 6 c, and the suspended PDP contexts may beresumed. If there are still usable direct connections between the mobilestation and the first RNC 502 and a working Iur interface between theRNCs, the first RNC may remain as a drifting RNC.

It is possible that the new SGSN is not capable of handling someinformation flows the controlling responsibility of which it hasreceived during the handover. Special measures which are as such outsidethe scope of the present invention may be taken in order to adapt theinformation flows to the capabilities of the new SGSN. After allinformation flows are in such shape that the new SGSN is capable ofhandling them, the connection between the mobile terminal and the oldSGSN may be terminated.

FIGS. 7 a and 7 b are simplified flow diagrams that show an importantdifference between a prior art method (FIG. 7 a) and a method accordingto the invention (FIG. 7 b) when handovers are concerned. In FIG. 7 aall QoS flows are active throughout the handover, and LLC layer routinesare employed to correct any errors that the handover causes to theerror-critical, delay-tolerant QoS flows. In FIG. 7 b a step 704 ofsuspending the selected error-critical, delay-tolerant QoS flowsprecedes the handover, no LLC layer routines are performed, and a step705 of resuming the error-critical, delay-tolerant QoS flows follows thehandover.

A comparison between FIGS. 1 and 4, with the help of FIGS. 2 and 3, maybe used to describe a mobile station and an SGSN according to theinvention. It is known as such that the advantageous implementation ofthe protocol stacks in mobile stations and SGSNs is in the form ofmicroprocessor-executable computer programs stored in memory devices. Byapplying the teachings of the present patent application it is withinthe capabilities of a person skilled in the art to realise, instead ofthe protocol structures illustrated in FIGS. 1 and 2, the protocolstructures according to FIGS. 3 and 4 so that the mobile stations andSGSNs with such an implementation will operate according to the presentinvention.

The invention has been desribed above solely with reference topacket-switched non-real time communication connections. However, it ispossible to apply the concept of suspending and releasing also tospecific kinds of circuit-switched connections. The prerequisite forapplying the invention to circuit-switched connections is that suchconnections must have very relaxed delay requirements; in theterminology of second generation digital cellular radio systems theinvention is applicable to non-transparent circuit-switched connectionsbut not to transparent circuit-switched connections because of the tightdelay requirements associated therewith.

1. A method for a mobile station for performing a handover from a firstnetwork connection to a second network connection in a mobiletelecommunication system providing for non-real time telecommunicationconnections over a radio interface between mobile stations and the fixedparts of the mobile telecommunication system, comprising in the orderrecited the steps of: suspending at least one active packet-switchednon-real time telecommunication connection between a mobile station andthe fixed parts of the mobile telecommunication system, performing ahandover from the first network connection to the second networkconnection, including exhausting through the first network connectionall transmission buffers that, at the time of suspending said at leastone active packet-switched non-real time telecommunication connection,contain data to be transmitted over the first network connection, andresuming the suspended non-real time telecommunication connection.
 2. Amethod according to claim 1, wherein the first network connection is aconnection from the mobile station via a first radio network controllerto a first serving node of a packet-switched data transmission networkand the second network connection is a connection from the mobilestation via a second radio network controller to said first servingnode, whereby the step of performing a handover comprises the substep ofestablishing the logical connections between the mobile station and saidfirst serving node via said second radio network controller thatconstitute the second network connection.
 3. A method according to claim2, wherein the first network connection is a macrodiversity connectioncomprising a direct connection between the mobile station and said firstradio network controller and an indirect connection between the mobilestation and the said first radio network controller via said secondradio network controller and the second network connection is amacrodiversity connection comprising a direct connection between themobile station and said second radio network controller and an indirectconnection between the mobile station and said second radio networkcontroller via said first radio network controller, whereby the step ofperforming a handover comprises additionally the substep of changing themacrodiversity control from the first radio network controller to thesecond radio network controller.
 4. A method according to claim 1,wherein the first network connection is a connection from the mobilestation via a first radio network controller to a first serving node ofa packet-switched data transmission network and the second networkconnection is a connection from the mobile station via a second radionetwork controller to a second serving node of said packet-switched datatransmission network, whereby the step of performing a handovercomprises the substep of establishing the logical connections betweenthe mobile station and said first serving node via said second radionetwork controller that constitute the second network connection.
 5. Amethod according to claim 1, wherein the non-real time telecommunicationconnections are arranged according to a certain structure of protocolstacks in a mobile station, a radio access network, a serving supportmode of a packet-switched data transfer network and a gateway supportmode of a packet-switched data transfer network, and the methodcomprises the steps of communicating between a number of first peerentities between the mobile station and the radio access network,wherein said first peer entities are composed of a physical layer, aMedia Access Control layer and a Radio Link Control layer, communicatingbetween a number of second peer entities between the radio accessnetwork and the serving support node of a packet-switched data transfernetwork, wherein said second peer entities are composed of a physicallayer, a Network Service layer and a protocol layer for communicationbetween the radio access network and the packet-switched data transfernetwork, and communicating between a number of third peer entitiesbetween the mobile station and the serving support node of apacket-switched data transfer network, wherein said third peer entitiesare composed of a Subnetwork Dependent Control Protocol Layer which inthe mobile station is immediately on top of the Radio Link Control layerand in the serving support node of a packet-switched data transfernetwork is immediately on top of the protocol layer for communicationbetween the radio access-network and the packet-switched data transfernetwork.
 6. A method according to claim 5, additionally comprising thesteps of performing error detection and error-related retransmission aswell as flow control between the mobile station and the radio accessnetwork in said Radio Link Control layer.
 7. A method according to claim1, wherein the first network connection and the second networkconnection are packet-switched connections for transmittingerror-critical data.
 8. A method according to claim 1, wherein the firstnetwork connection and the second network connection are non-transparentcircuit-switched connections.
 9. A mobile station for communicating withthe fixed parts if a mobile telecommunication system over networkconnections, comprising means for executing the method according toclaim 1 in order to perform a handover from a first network connectionto a second network connection.
 10. A method for a mobile station forperforming a handover from a first network connection to a secondnetwork connection in a mobile telecommunication system providing fornon-real time telecommunication connections over a radio interfacebetween mobile stations and the fixed parts of the mobiletelecommunication system, comprising in the order recited the steps of:suspending at least one active non-real time telecommunicationconnection between a mobile station and the fixed parts of the mobiletelecommunication system, performing a handover from the first networkconnection to the second network connection, and resuming the suspendednon-real time telecommunication connection; wherein the first networkconnection is a connection from the mobile station via a first radionetwork controller to a first serving node of a packet-switched datatransmission network and the second network connection is a connectionfrom the mobile station via a second radio network controller to saidfirst serving node, whereby the step of performing a handover comprisesthe substeps of: exhausting through the first network connection alltransmission buffers that, at the time of suspending said at least oneactive non-real time telecommunication connection, contain data to betransmitted over the first network connection; and establishing thelogical connections between the mobile station and said first servingnode via said second radio network controller that constitute the secondnetwork connection.
 11. A method according to claim 10, wherein: thefirst network connection is a macrodiversity connection comprising adirect connection between the mobile station and said first radionetwork controller and an indirect connection between the mobile stationand said first radio network controller via said second radio networkcontroller; and the second network connection is a macrodiversityconnection comprising a direct connection between the mobile station andsaid second radio network controller and an indirect connection betweenthe mobile station and said second radio network controller via saidfirst radio network controller, whereby the step of performing ahandover comprises additionally the substep of changing themacrodiversity control from the first radio network controller to thesecond radio network controller.
 12. A method according to claim 10,wherein the first network connection is a connection from the mobilestation via a first radio network controller to a first serving node ofa packet-switched data transmission network and the second networkconnection is a connection from the mobile station via a second radionetwork controller to a second serving node of said packet-switched datatransmission network, whereby the step of performing a handovercomprises the substeps of: exhausting through the first networkconnection all transmission buffers that, at the time of suspending saidat least one active non-real time telecommunication connection, containdata to be transmitted over the first network connection; andestablishing the logical connections between the mobile station and saidsecond serving node via said second radio network controller thatconstitute the second network connection.
 13. A method according toclaim 10, wherein the non-real time telecommunication connections arearranged according to a certain structure of protocol stacks in a mobilestation, a radio access network, a serving support node of apacket-switched data transfer network and a gateway support node of apacket-switched data transfer network, and the method comprises thesteps of: communicating between a number of first peer entities betweenthe mobile station and the radio access network, wherein said first peerentities are composed of a physical layer, a Media Access Control layerand a Radio Link Control layer, communicating between a number of secondpeer entities between the radio access network and the serving supportnode of a packet-switched data transfer network, wherein said secondpeer entities are composed of a physical layer, a Network Service layerand a protocol layer for communication between the radio access networkand the packet-switched data transfer network, and communicating betweena number of third peer entities between the mobile station and theserving support node of a packet-switched data transfer network, whereinsaid third peer entities are composed of a Subnetwork Dependent ControlProtocol Layer which in the mobile station is immediately on top of theRadio Link Control layer and in the serving support node of apacket-switched data transfer network is immediately on top of theprotocol layer for communication between the radio access network andthe packet-switched data transfer network.
 14. A method according toclaim 13, additionally comprising the steps of performing errordetection and error-related retransmission as well as flow controlbetween the mobile station and the radio access network on said RadioLink Control layer.
 15. A method according to claim 10, wherein thefirst network connection and the second network connection arepacket-switched connections for transmitting error-critical data.
 16. Amethod according to claim 10, wherein the first network connection andthe second network connection are non-transparent curcuit-switchedconnections.
 17. A mobile station for communicating with the fixed partsof a mobile telecommunication system over network connections,comprising means for executing the method according to claim 10 in orderto perform a handover from a first network connection to a secondnetwork connection.
 18. A method for a mobile station for performing ahandover from a first network connection to a second network connectionin a mobile telecommunication system providing for non-real timetelecommunication connections over a radio interface between mobilestations and the fixed parts of the mobile telecommunication system,comprising in the order recited the steps of: suspending at least oneactive non-real time telecommunication connection between a mobilestation and the fixed parts of the mobile telecommunication system,performing a handover from the first network connection to the secondnetwork connection, and resuming the suspended non-real timetelecommunication connection; wherein the first network connection is aconnection from the mobile station via a first radio network controllerto a first serving node of a packet-switched data transmission networkand the second network connection is a connection from the mobilestation via a second radio network controller to a second serving nodeof said packet-switched data transmission network, whereby the step ofperforming a handover comprises the substeps of: exhausting through thefirst network connection all transmission buffers that, at the time ofsuspending said at least one active non-real time telecommunicationconnection, contain data to be transmitted over the first networkconnection; and establishing the logical connections between the mobilestation and said second serving node via said second radio networkcontroller that constitute the second network connection.
 19. A methodaccording to claim 18, wherein the non-real time telecommunicationconnections are arranged according to a certain structure of protocolstacks in a mobile station, a radio access network, a serving supportnode of a packet-switched data transfer network and a gateway supportnode of a packet-switched data transfer network, and the methodcomprises the steps of: communicating between a number of first peerentities between the mobile station and the radio access network,wherein said first peer entities are composed of a physical layer, aMedia Access Control layer and a Radio Link Control layer, communicatingbetween a number of second peer entities between the radio accessnetwork and the serving support node of a packet-switched data transfernetwork, wherein said second peer entities are composed of a physicallayer, a Network Service layer and a protocol layer for communicatingbetween the radio access network and the packet-switched data transfernetwork, and communicating between a number of third peer entitiesbetween the mobile station and the serving support node of apacket-switched data transfer network, wherein said third peer entitiesare composed of a Subnetwork Dependent Control Protocol Layer which inthe mobile station is immediately on top of the Radio Link Control layerand in the serving support node of a packet-switched data transfernetwork is immediately on top of the protocol layer for communicationbetween the radio access network and the packet-switched data transfernetwork.
 20. A method according to claim 19, additionally comprising thesteps of performing error detection and error-related retransmission aswell as flow control between the mobile station and the radio accessnetwork on said Radio Link Control layer.
 21. A method according toclaim 18 wherein the first network connection and the second networkconnection are packet-switched connections for transmittingerror-critical data.
 22. A method according to claim 18, wherein thefirst network connection and the second network connection arenon-transparent circuit-switched connections.
 23. A mobile station forcommunicating with the fixed parts of a mobile telecommunication systemover network connections, comprising means for executing the methodaccording to claim 18 in order to perform a handover from a firstnetwork connection to a second network connection.